We study in vitro differentiation of different cell types from ethylnitrosourea-induced rat neurotumors. Biochemical cytological characterization of several cell lines clonally isolated from a rat neurotumor RT4 are conducted on their neuronal and glial properties. Particular interest is on the phenomenon of "cell-type conversion" we have discovered, in which a multipotential stem cell line converts to three different cell types in culture and these derivative cell types posses either glial (S100) or neuronal (voltage-dependent Na ion influx) properties. Polulation-wise, the stem cells have both properties. Several known glial and neuronal properties will be examined in these cell lines. Cytochemical analyses of the individual cells of the stem-cell population will be made. Various culture conditions that may influence the rate and direction of cell-type conversion will be examined. Another phenomenon we have noticed is "conversion coupling," in which a specific combination of two or more differentiated characteristics are expressed in a stem cell-derived cell type. This is extremely important for the in vitro studies of cell differentiation and will be studied in detail. Cloning of a few additional neurotumors of central and peripheral nerve origins will also be performed to establish new families of neurocell types which are related by cell-type conversion of stem cells.